In Japan, a large number of businesses are engaged in manufacturing industries of various types that support the foundations of industry, such as semiconductor manufacturing, electronic and electrical goods manufacturing, precision machinery manufacturing, transport equipment manufacturing, chemical manufacturing, fiber manufacturing, ceramics manufacturing, medical product manufacturing, foodstuff manufacturing and so on. In workplaces that are in charge of actual manufacture in this type of manufacturing industry, the manufactured products are assembled by automatic processing or by manual processing while many components flow along a production line.
Now, if there is a fault or a defect in one of the components that go into the manufactured product, or if there is a malfunction or a defect in the manufacturing process, then naturally a faulty or defective manufactured product will be the result, and there is the problem that the manufacturing yield decreases. Or, even if there is no problem with any component, sometimes faults or defects occur in the product after manufacture for various reasons. In relation both to the former and the latter cases, there are the problems that, in an automated manufacturing process, if an operational fault occurs in some step of the process, then the manufacturing speed (i.e. the manufacturing efficiency) drops, and/or the manufacturing yield of the final manufactured product is deteriorated.
In the prior art, centering upon large companies, there have been many cases in which a series of flows from research through development, design, manufacture, and quality control to sales have been performed in a vertically integrated manner. Businesses of this vertically integrated type are environments in which it is easy for responses in development and design in relation to quality shortcomings and reductions of yield rate of manufactured goods (both finished products and part-finished products) that occur in a manufacturing site to be fed back and/or fed forward within the same company.
On the other hand, in recent years, manufacturers (i.e. manufacturing plants) are being converted into subsidiary companies due to problems of manufacturing costs when they are together in the same business, and also manufacturing companies that only perform contract manufacturing are appearing. In a similar manner, “fabless” businesses and so on that only perform research and development but do not perform manufacture also are flourishing in the fields of electronics, information and communication, and so on.
In this manner, in current manufacturing industry, there is an increasing physical, temporal, technical, and human dissociation between the area of development and design and the area of actual manufacturing. When there is such a dissociation, feed back and feed forward between a manufacturing site and a development site become difficult in relation to poor product quality and deterioration of yield rate occurring in the manufacturing site. Because of this difficulty, there is a concern that manufacturing capacity in Japanese manufacturing industry (including contract manufacturers that only perform manufacture to contract, manufacturing subsidiaries, fabless businesses and so on) is declining.
There can be various causes of deterioration in product quality and yield rate at a manufacturing site. Some causes are inevitable, such as poor ease of design and manufacture, level of experience of the manufacturing site, manufacturing process flow, manufacturing equipment, human skills, and so on, but a cause that is often overlooked is static electricity. In other words, there are causes of various kinds that can lead to faults or defects in components, manufactured products or manufacturing processes of this type, but static electricity is also considered as being one possible cause.
In a manufacturing facility, in consideration of adverse effects of this type upon components, manufactured products, manufacturing processes and so on due to static electricity, means have been devised for prevention of static upon factory buildings, floors, walls and so on and for preventing buildup of static electricity upon the clothing of workers, and means have been implemented in order for static electricity not to exert any influence upon components, manufactured products, manufacturing processes and so on. In concrete terms, static electricity has been eliminated from floor surfaces, walls, conveyor lines and so on before working starts, grounds have been provided for discharging static electricity, and contrivances have been implemented in order for static electricity not to build up upon parts used in the manufacturing process or upon the manufactured products.
Furthermore, in manufacturing plants, means have also been devised for eliminating static electricity in advance from components to be used in the manufacturing process. And, in a similar manner, operators are also performing measures for only starting work after elimination of static electricity.
In this manner, in manufacturing plants, contrivances of various types have been implemented for suppressing the negative influence of static electricity. Despite this ingenuity, the problem of buildup of static electricity upon parts used in manufacturing processes and upon the manufactured products is not yet perfectly solved. For example, there is steady progress in reduction of power consumption in electronic equipment and precision equipment and so on made in manufacturing plants. Along with the reduction of power consumption, the capability of components that are used in the manufacture of such electronic equipment and precision equipment for resisting static electricity is undesirably decreasing. Due to this, the components used in the manufacture of such electronic equipment and precision equipment often become charged with static electricity and can easily become faulty.
There are various kinds of components that are used in the manufacture of such electronic equipment and precision equipment. For example, parts made from resin or vinyl (such as connectors, covers for screens, casings and so on) are also used in many ways. These components have a certain size, and, if they become charged with static electricity, this may sometimes engender unpredictable behavior.
For example, a plurality of components may flow in a conveyor line and may enter a process in which they are arranged in fixed positions, or may enter into a process of visual testing by image processing. In a process of this type, it is desirable for the plurality of parts that have been put onto the conveyor line to flow in the conveyor line while appropriate feeding intervals between them are maintained.
However, if such parts are electrostatically charged, then behavior on the conveyor line such as parts getting closer to one another due to static electricity or repelling one another and moving further apart or the like may occur. In some circumstances, adjacent parts may actually stick together. When this type of behavior takes place, appropriate processing for implementing the arrangement process or the external visual testing process described above may undesirably become impossible, and sometimes it may happen that a product is automatically determined as being defective, even though actually it is good.
If such unpredictable behavior of components undesirably takes place in the arrangement process or the external visual inspection process, then it is necessary to stop the conveyor line temporarily. It can be predicted that this type of behavior may be caused by electrostatic charge, but, as a countermeasure, there is no choice but to eliminate static electricity from the conveyor line, from all the processing equipment, and from all parts fed onto the conveyor line. If the conveyor line is stopped due to this type of static electricity elimination task, a large loss will eventuate to the manufacturing plant. Manufacturing operation stops during the task of static electricity elimination (which, depending upon the circumstances, may occupy half a day or a full day).
It is known that static electricity is the cause for components to exhibit behavior of the type described above, but the actual mechanism that leads to such behavior has not really been elucidated. In particular, sometimes components may exhibit different behaviors such as approaching toward one another or moving apart or the like, and sometimes they may exhibit no unusual behavior at all. Due to this fact, it is difficult to clarify the mechanisms that lead to such behavior, because it is not known how the static electricity (surmised to be) charged upon the components is distributed upon the components. If it is difficult to elucidate the mechanism, then it is also of course impossible to investigate countermeasures for preventing behavior of the sort described above.
Additionally, covers made from resin or vinyl or the like that are attached to the screens of portable telephones and smart phones and so on are liable to become charged with static electricity due to their material and their area. If such a component is employed in the process of assembly of an electronic device or a precision device, then, if the component is still charged with static electricity, then sometimes it may happen that, due to its electrostatic charge, the position in which it is installed may deviate in an arbitrary manner, which is undesirable. A device during the assembly of which this type of deviation has happened naturally turns out to be defective.
In this case as well, it can be surmised that accumulation of electrostatic charge upon the component is the cause, but the relationship between the behavior and the electrostatic charge is unknown. It is impossible to anticipate resolution of the problem if this relationship is not known. In other words, clear understanding of how a component or the like becomes charged with static electricity is a prerequisite for solution of such problems that arise in a manufacturing process. To put this in another manner, for it to be possible to check the nature of the distribution in which static electricity is charged upon a component or the like is a precondition for clarifying the behavior of the component.
Furthermore, in devices such as printers that take advantage of static electricity, it is necessary to verify the static electricity distribution of parts that utilize electrostatic charging.
In this manner, as a precondition for solution of problems of various types in manufacturing processes and so on that are considered to be caused by static electricity, and as a precondition for checking the performance and characteristics of components that utilize static electricity, it is desirable to be able to measure the electrostatic charge amount distribution upon a component or the like accurately and also quickly.
As devices for measuring amounts of electrostatic charge of this type, there have been proposed a surface electrometer or an electrostatic force microscope, or a electrostatic charge amount measuring device etc. that calculates an amount of electrostatic charge by measuring, as a change in potential, a virtual electromagnetic wave generated by vibration imparted to the measurement subject (for example, refer to Patent Documents #1 and #2).